1. Field of the Invention
The present invention relates to a method and apparatus for converting a moving image, a method and apparatus for reproducing a moving image, and a computer program. In particular, the present invention relates to a method and apparatus for converting a moving image, a method and apparatus for reproducing a moving image, and a computer program for performing a high-quality data conversion in a manner free from image degradation in data compression process of moving image data.
2. Description of the Related Art
When moving image data is stored onto a recording medium such as a hard disk (HD), a digital versatile disk (DVD), a Blu-ray disk (a next-generation disk) or is distributed over a network, a data conversion for reducing an amount of the data, for example, a compression process is performed on the data. Today, quality of the moving image data has been substantially improved. For example, high-definition data is in widespread use. As the high-quality data is used, an amount of data handled is also increased. Techniques for improving compression efficiency in the compression process of the moving image data and preventing the data from being degraded in the course of the compression process have been studied.
The compression methods of a moving image includes a decimation process for decimating pixels forming an image frame of the moving image data, namely, a spatial decimation process, and a frame rate reduction process, namely, a decimation process in time axis.
Data amount reduction in the data conversion allows the data to be stored efficiently onto a recording medium or to be transferred efficiently via a network. When the compressed data is then reproduced, image degradation takes place. If original image data has a high resolution, the degree of image degradation becomes pronounced.
A variety of techniques have been studied to reduce such an image degradation. Japanese Unexamined Patent Application Publication No. 2005-198268 discloses an image compression process technique that switches between a pixel count decimation process in a spatial direction and a pixel count decimation process in a time direction in response to the magnitude of a movement speed of a subject. Japanese Unexamined Patent Application Publication No. 2006-5904 discloses a technique that further changes phase at a sampling point in response to a movement speed of a subject in the pixel count decimation process in the spatial direction in addition to the technique disclosed in Japanese Unexamined Patent Application Publication No. 2005-198268.